Properly escape backslashes in some regexes

[mih]

Fixes #5985

[codecov]

Codecov Report

Merging #6147 (d9fd85c) into master (3cbc5cd) will decrease coverage by 2.60%.
The diff coverage is 50.00%.

❗ Current head d9fd85c differs from pull request most recent head 36f3155. Consider uploading reports for the commit 36f3155 to get more accurate results

@@            Coverage Diff             @@
##           master    #6147      +/-   ##
==========================================
- Coverage   89.76%   87.16%   -2.61%     
==========================================
  Files         318      318              
  Lines       41855    41863       +8     
==========================================
- Hits        37571    36489    -1082     
- Misses       4284     5374    +1090     

Impacted Files	Coverage Δ
datalad/tests/test_log.py	93.05% <50.00%> (-6.25%)	⬇️
datalad/version.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/wtf.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/addurls.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/no_annex.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/distribution/drop.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/add_readme.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/check_dates.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/distribution/remove.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/support/tests/utils.py	0.00% <0.00%> (-100.00%)	⬇️
... and 134 more

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